Alzheimer's Disease (AD) is a progressive form of presenile neuropathy which causes chronic symptoms of serious neurodegeneration, and which is prone to progress to dementia. The recognition and intelligence functions of AD patients are seriously destroyed. The disease is the main cause of adult dementia and it is estimated that about 2.5 million individuals are infected with such disease in the United States and Canada. With the growth of senile population, it is expected that the impact of AD on public health will continuously increase. Accordingly, the development of effective medicines for AD therapy is in urgent need.
Tacrine, also known as 1,2,3,4-tetrahydro-9-acridinamine hydrochloride (THA), is a reversible acetyl cholinesterase inhibitor which may increase cerebral acetyl choline concentration, in particular in the cerebral cortex, by counteracting the destruction of acetyl choline by acetyl cholinesterase. Tacrine has been approved by U.S. Food and Drug Administration (FDA) for use in AD therapy in 1993, and is the only agent for treating mild to medium AD. It can significantly improve the memory and recognition of patients.
Tacrine has also been used as the analgesic for end-staged cancers, myasthenia gravis, tricyclic anti-depressive agent toxication and tardive dyskinesia.
It is known that tacrine may cause reversible hepatoxicity and many adverse effects, e.g. gastro-intestinal side effects, such as nausea, vomiting, diarrhea, dyspepsia and loss of appetite; kinetic ataxia of voluntary muscles and myalgia; sweating and bradycardia induced by overexcitement of vagus nerues.
The conventional preparations of tacrine should be administered four times a day. The compliance to senile people is therefore poor. Moreover, the pharmacokinetics of tacrine reveal that the oral bioavailability of tacrine may significantly vary in different individuals, and patients should experience a dosage adjustment period.
Accordingly, it is desired in the art to develop controlled release dosage forms of tacrine in order for maintaining stable concentration of the medicine in blood and brain to lower side effects, and for reducing the administration frequency to increase the compliance of the medicine, in particular to senile people.
U.S. Pat. No. 5,576,022 discloses a controlled release tacrine drug delivery system comprising immediate release pellets and sustained release pellets. The immediate release pellets are formed by coating non-pareil seeds with a coating comprising tacrine and a binder, and then with a coating comprising a sealing agent and a plasticizing agent. The sustained release pellets are formed by coating the immediate release pellets with a sustained release coating comprising a water insoluble polymer, a water soluble polymer and a second plasticizing agent.
The delivery system of the above patent may control the release of tacrine. However, as the sustained release pellets are multilayered, the preparation procedures are complex. In addition, as the size of the immediate pellets and the sustained release pellets are different, it would be inconvenient to fill them into capsules.